Devices of this type are used in particular, but by no means exclusively, in the mechanical square-edging of fabric webs. In order to turn over the longitudinal edge, the fabric web being folded over once or a number of times parallel to the longitudinal edge, the fabric web is conveyed, for example drawn, through an edge turning device in the direction of the longitudinal edge by means of a conveying device. Arranged in the edge turning device are two guide elements, which each come to rest against one side of the fabric web in the region of a longitudinal edge section. In other words, the two guide elements rest against the longitudinal edge from above and below, so that the fabric web slides along the guide surfaces in the region of the longitudinal edge as it is conveyed through the edge turning device and is thereby shaped, guided by the guide surfaces.
In order to attain the desired folding of the fabric web parallel to the longitudinal edge, the guide surface of the guide element abutting from the inside is convex and the guide surface of the guide element abutting from the outside is concave in construction. In this manner, the opposing guide surfaces form a gap, whose width is at least slightly larger than the thickness of the fabric web in the region of the longitudinal edges, so that this gap is filled in its cross section by the longitudinal edge of the fabric web and effects the turning over of the longitudinal edge during the conveyance of the fabric web through the edge turning device.
A disadvantage in these known devices is that it is only possible to process materials of like thickness using the known edge turning devices. Since the two guide elements of the known edge turning devices are rigidly secured, for example by being fixedly soldered to a support plate, the width of the gap is preset. However, in order to ensure disturbance-free processing of the fabric web, it is necessary for the surfaces of the fabric web to rest closely against both guide surfaces, which is the reason why with the known devices it is only possible to process materials whose thickness varies to a very small degree. If materials having different thicknesses are to be processed, then it is necessary in each case to replace the edge turning devices according to the material thickness.